Liquid crystals are commonly used to construct displays used in a wide variety of electronic devices, such as digital watches, calculators, handheld mobile phones, miniature television sets as well as large, flat projection screens for home entertainment systems, liquid-crystal computer displays for portable computers, and optical devices.
Liquid crystal-based devices are typically formed on a silicon wafer 100, as shown in FIG. 1, including a plurality of dies 110A-110N, such as die #1 to die #9, for example, using an emerging display technology, known as liquid crystal-on silicon (LCOS). Each die 110A-110N on the silicon wafer 100 may be provided with an active matrix of displaying processing functions of a micro LCOS device, and one or more integrated circuit (IC) chips such as microprocessors, chipsets, system on-chips, application specific integrated circuits (ASICs), digital signal processing (DSP) systems and other types of programmable logic arrays or devices. In general, the entire silicon wafer 100 including a plurality of dies 110A-110N and the cover glass (not shown) are assembled for mass production.
FIG. 2 illustrates an example flow diagram of a current process of manufacturing LCOS devices from a silicon wafer shown in FIG. 1. As shown in FIG. 2, the silicon wafer 100 including a plurality of dies 110A-110N shown in FIG. 1, and the cover glass (not shown) are received separately at block 210. The cover glass is then assembled on the silicon wafer to form a silicon-glass assembly at block 220. The silicon-glass assembly is then singulated, or broken and separated into individual die at block 230. After individual dies are separated from the assembled wafer, each die is filled with a liquid crystal material, end-sealed at block 240, and then wire-bonded and assembled into a LCOS device at block 250. Subsequently, each LCOS device may be tested both for electrical functionality (i.e., if there is no electrical disconnect or short circuit) and imager functionality (i.e., if an image follows specification) before functioning units can be packaged into a flex cable or assembled into any other package with a variety of different contacts for connecting to the outside world.
However, current methods of mass production of LCOS devices suffer a number of disadvantages. First, the liquid crystal fill is done on die level after singulating the cover glass and individual die from the wafer. This is prone for contamination in cell gap due to debris from singulation, which interferes with subsequent processing of LCOS devices. Secondly, the electro-optical testing of individual micro LCOS devices is done after silicon backplane assembly and assembly of each die into LCOS devices. Extensive backplane assembly can be costly and time consuming due to its requirements for expensive equipment, long processing times, and control of many process variables. Moreover, the electro-optical testing of individual micro LCOS device after assembly of die into LCOS devices is not desirable or manufacturable due to high cost and low yield as all dies are assembled irrespective of whether an individual die is functional or not.
Therefore, a need exists for a more efficient method of mass production of LCOS devices with a simpler and more direct wafer level liquid crystal filling process, a cleaner cover glass singulation process and an electro-optical sorting and testing of LCOS devices at wafer level for identification and assembly of a good die